1. Field of the Invention
This invention relates to semiconductor devices and processes for their manufacture, and more specifically relates to a trench type MOSFET with reduced RDSON and improved reverse recovery characteristics.
2. Description of the Related Art
High voltage superjunction MOSFET devices are well known. Such devices are usually made by a process in which multiple epitaxially grown layers with respective aligned P diffusions (for an N channel device) are formed to define spaced, elongated P type pylons or columns in an N type epitaxially grown substrate (N epi). These P type pylons are in charge balance with the surrounding N epi and, as a result, the concentration of the N epi can be increased, as compared to that of a conventional MOSFET, to reduce on resistance (RDSON).
This process is complex and requires a large inventory of epitaxial reactors and a large number of process steps. Further, the breakdown voltage of the superjunction device is very sensitive to the charge balance. Thus, a 10% deviation from an optimum design can defeat production of acceptable devices.
It would be very desirable to provide a device which can be made by a simpler process which has the benefits of the superjunction device but without the need for multiple epitaxial depositions and charge balance control.